Signal modulation plays a key role in many electronic applications, especially those relating to communications where modulation techniques facilitate transmitting and receiving wired and wireless communication signals. Use of modulation techniques is common not only in communications over coaxial cable and twisted pair cables, but also in over-the-air communications at microwave and satellite frequencies. Typically, several stages of signal modulation are involved in transmitting a communications signal from one location and receiving the communications signal at another location. This is often the case for microwave communications, where it can be necessary to transmit a communications signal from a remote site to a local office using a microwave communications system, and then transmit the communications signal from the local office to customer premise equipment (CPE) over a cable.
Traditional signal receivers, particularly those configured to receive wireless signals (e.g., at radio frequencies such as microwave or millimeter wave), employ a heterodyne system to convert a signal from one frequency to another frequency during signal processing. For instance, when a conventional microwave system receives a signal at a microwave frequency, the system translates the signal from the microwave frequency to a lower frequency optimized for transmission over a cable medium. Conventional microwave systems typically perform this translation by converting the radio frequency (RF) signal (in this case at a microwave frequency) to an intermediate frequency (IF) that can be better modulated over cable mediums.
FIG. 1 illustrates one such conventional heterodyne system 100 configured to convert a radio frequency signal 102 to an intermediate frequency signal 120. In particular, the heterodyne system 100 illustrates a double downconversion heterodyne system, where the radio frequency signal 102 is first downconverted to a first intermediate frequency signal 110 for purposes of image filtering, before being downconverted to the second intermediate frequency 120 for subsequent signal processing (e.g., data demodulation and/or carrier recovery). As illustrated, the conventional heterodyne system 100 performs the double downconversion by amplifying the radio frequency signal 102 with an amplifier 104 and then (at a mixer 106) mixing the resulting, amplified radio frequency signal with an oscillator signal (at a frequency F1) generated by a oscillator 108. The mixing results in the first intermediate frequency signal 110 (IF1), which is subsequently filtered by a filter 112 (e.g., for image filtering) and amplified by an amplifier 114 before being mixed (at a mixer 116) with an oscillator signal (at a frequency F2) generated by another oscillator 118. From the mixer 116, the second intermediate frequency signal 120 is produced. Following further amplification, the second intermediate frequency signal 120 would be ready for further demodulation and/or carrier recovery processes.